1. Field of the Invention
The present invention relates to a light guide in which light-scattering particles are contained in an optical medium so that light which enters the light guide from an end face can propagate to another end face while being scattered by the light-scattering particles. The present invention also relates to a method for designing the above light guide.
2. Description of the Related Art
The following documents (1) to (4) disclose information related to the present invention.
(1) Japanese Registered Patent No. 3162398 (pages 7 through 9 and FIG. 3) 
(2) Japanese Registered Patent No. 3184249 (pages 9 through 11 and FIGS. 1 and 3) 
(3) Japanese Registered Patent No. 3215218 (pages 10 through 11 and FIGS. 2 and 8) 
(4) Japanese Unexamined Patent Publication NO. 10-123350 (pages 5 through 7 and FIGS. 3 through 6) 
As indicated in documents (1) and (2), light guides in which light-scattering particles are contained in an optical medium such as PMMA (polymethyl methacrylate) so that light which enters the light guide from an end face can propagate to another end face while being scattered by the light-scattering particles are known.
In the above light guides, light propagates while repeating reflection by the light-scattering particles in the optical medium as well as total reflection at interfaces between side ends of each light guide and an ambient medium (e.g., air or a cladding layer) around the light guide. Therefore, it is possible to output light having a more uniform intensity from a light-emission end face, in comparison with the light guides in which light propagates without the reflection by the light-scattering particles.
In an application utilizing the above advantage, which has been considered as disclosed in document (4), an optical data bus is constructed by coupling an input unit to an end face of a light guide containing light-scattering particles as above so as to input an optical signal through the input unit, and coupling a plurality of output units to another end face of the light guide so as to deliver the optical signal as a common signal to the plurality of output units.
Further, as disclosed in documents (1) to (3), it has also been considered to use a light guide containing light-scattering particles as described above for generating uniform illumination light with satisfactory light propagation efficiency in a liquid crystal display device or the like.
Conventionally, it is impossible to easily obtain a design condition which realizes a desired light-output efficiency and a uniform emission-intensity distribution. Therefore, for example, the following methods (a) and (b) are used.
(a) In the first method, in order to obtain a light guide having desired characteristics, a plurality of samples of a light guide respectively having different diameters and densities of particles contained in optical mediums are produced, and one of the samples which realizes a desired light-output efficiency and a uniform emission-intensity distribution is chosen for use.
(b) In the second method, a design condition is determined by extensive simulation using a computer system.